The present invention relates to a liquid crystal image display apparatus which can display an image with a low power consumption.
Hereafter, an example of a display apparatus will be explained with reference to FIG. 23, which shows the configuration of the conventional TFT liquid crystal display apparatus. A typical display pixel 200 has a liquid crystal capacity 201 and a pixel switch 202, and the pixels are arranged in the form of a matrix. The gate of each pixel switch 202 is connected to gate line shift register 204 through a gate line 203. Moreover, in each pixel, one end of pixel switch 202 is connected to one of the DA converters 206A, 206B through a signal line 205. A line memory 207A, 207B is connected to a DA converter 206A, 206B, and the display data on input line209A, 209B is applied under control of the shift register 208A, 208B to the line memory 207A, 207B. Each of the above-mentioned circuit parts is formed on the same substrate by using polysilicon TFT.
In this arrangement, a separate pixel drive circuit composed of a DA converter 206, a line memory 207 and a shift register 208, as shown in the figure, has been provided above and below the pixel area; for instance, a signal line 205 of an odd number row is connected to an upper driving circuit and signal line 205 of an even number row is connected to a lower driving circuit.
Next, the operation of the apparatus of FIG. 23 will be explained.
The digital display data is input in series through the display data input lines 209A, 209B to the shift registers 208A, 208B and is written in the line memories 207A, 207B one by one by the shift registers 208A, 208B. Next, the display data stored in the line memories 207A, 207B is input to the DA converters 206A, 206B in parallel. The DA converters 206A, 206B output this data on signal lines 205 as a voltage of an analog image signal. At this time, when pixel switch 202 of a fixed display pixel line 203 selected by gate line shift register 204 turns on, the voltage of an analog image signal is written in the capacity 201 of the liquid crystal of the selected display pixels. This TFT liquid crystal panel displays the image based on the input display data according to the operation described above. Signal line 205 of the odd number row is connected to an upper driving circuit, and signal line 205 of the even number row is connected to a lower driving circuit, as described above. Therefore, the upper and lower driving circuits are synchronously driven, and the display of one screen is allotted to the upper and lower driving circuits.
Here, because the upper and lower circuits operate to drive a pixel under the same condition, both have basically the same circuit structures. An example of this display apparatus is described in detail in ISSCC (International Solid-State Circuits Conference) 2000, Digest of technical papers, pp.188-189.
The demand for installation of a high-definition image display panel which uses a number of pixels exceeding that of QCIF (Quarter common intermediate format 144 176 pixels) and CIF (288 352 pixels) for a portable information device along with the practical use of IMT-2000(international Mobile Telecommunications 2000) is increasing. There is also a demand for reducing the weight of a portable information device by reducing the weight of the secondary cell in one side. The demand for producing an image display unit having a low power consumption also has strengthened day by day at the same time.
On the other hand, it has been very difficult to realize a display image of high definition and low power consumption at the same time by using the above-mentioned conventional techniques. The reason is that the operation frequency of the liquid crystal panel increases and power consumption increases inevitably if a high definition display image is produced by an increase in the number of pixels.